Liquid phase oxidation of olefins using nitrobenzene to inhibit polymer formation



Feb. 5, 1957 H. GARDNER ET AL 2,780,635 LIQUID PHASE OXIDATION OF OLEFINS USING NITROBENZENE TO INHIBIT POLYMER FORMATION Filed Dec. 28, 1953 {Pressure Relief Valve Venl' 1 Cooling 1 Condenser OM \v -Reflux A Fleoc lor Temp. |3o-3ooc J I4 Pressure l 300 psig w I Disl'illal'ion Healfler Sepqmfio" Reocl'ion x Appqmhs {Produc'l's Solv'enl' Propylene Reucl'ion ll Producl's Propylene J ll A L Anhydrous Solvenl' 1 Air and Propylene -"Inhibi+or (e.g. Nil'robenzene) INVENTOR$ ATTORNEY U d a s Pat ce 2,780,635 Patented F eb. 5, 1951 LIQUID PHASE OXIDATION OF OLEFINS USING fiIE EIOIlgINZENE T INHIBIT POLYMER FOR- O James H. Gardner, Cambridge, and Nat C. Robertson, Wellesley, Mass., assignors, by mesne assignments, to Escambia Chemical Corporation, Pace, Fla., a corporation of Delaware Application December 28, 1953, Serial N 0. 400,432 4 Claims. (Cl. 260-3485) This invention relates to the production of chemicals and in particular to the production of olefin oxides. This application is, in part, a continuation of our copending application, Serial No. 316,158, filed October 22, 1952.

A principal object of the present invention is to produce oxygenated hydrocarbons in good yields by the liquid phase oxidation of normally gaseous hydrocarbons in a water-immiscible organic solvent with an elemental-oxygen-containing gas.

Another object of the present invention is to provide improved processes for the manufacture of olefin oxides from olefins.

Still another object of the present invention is to provide a process of the above type which is particularly adapted to the production of oxygenated hydrocarbons containing at least three carbon atoms, and in particular propylene oxide, by the oxidation of propylene.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and the order of one or more of such steps with respect to each of the others which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing which is a diagrammatic flow sheet illustrating one embodiment of the invention.

In the present invention, a normally gaseous, olefinic hydrocarbon containing at least three carbon atoms and above is oxidized at a relatively high pressure to give a high yield of the corresponding olefin oxide. A specific preferred embodiment includes propylene as the olefin to be converted to propylene oxide. This invention will be initially described in connection with the oxidation of propylene without intending to limit the scope thereof.

The oxidation is preferably achieved by passing an elemental-oxygen-containing gas upwardly through a liquid phase containing the olefin to be oxidized (e. g., propylene). This liquid phase is preferably a waterimmiscible organic solvent which is preferably relatively inert to oxygen under the reaction conditions. A preferred solvent is benzene. The oxygen-containing gas is preferably air which is introduced through an air disperser into the reactor.

, In order to obtain a high yield of the olefin oxide (e. g., propylene oxide) in preference to the corresponding glycol, it is preferable that the oxidation be carried out (a) at high concentrations of the olefin (e. g., propylene) in the solvent, (b) in the absence of appreciable quantities of water, and (c) in a substantially neutral solution.

In one preferred embodiment of the invention, it has been found desirable to maintain the water-immiscible organic solvent as nearly saturated as possible with the olefin (e. g., propylene) during the oxidation. At the preferred reaction conditions, best results are obtained by maintaining the mole percent of the olefin preferably above about 30% of the solvent.

It has also been found desirable to carry out the olefin oxidation in the presence of a minimum quantity of water. By maintaining a low water concentration in the reaction zone during the oxidation, hydrolysis of the oxide to the glycol is drastically reduced. It is, therefore, preferable that the amount of water present in the reaction zone at any one time be maintained less than about 10% by weight of the water-immiscible solvent. Hydrolysis of the olefin oxide is also reduced by carrying out the oxidation. under substantially neutral conditions. Thus, it is preferred that the reaction mixture be maintained substantially neutral during the oxidation.

In the preferred embodiment of the invention, the conditions of reaction are so adjusted that polymerization of the feed and/or the various intermediate by-products of the reaction is minimized. This polymerization is preferably reduced by the use of an inhibitor such as nitrobenzene.

This invention will be particularly described in connection with the oxidation of propylene to propylene oxide. The reference numerals in the following nonlirniting example, indicate the appropriate sections of the flow sheet illustrated in the drawing:

Example I The solvent, 1350 mls. of benzene, together with 1.4 grams of a manganese propionate catalyst and 120 grams of nitrobenzene buffered to a pH 6.5 with 102 cc. of a phosphate buffer solution were charged to a high pressure reactor 10. 313 grams of propylene were then 7 passed into the reactor 10. The reactor was put under about 300 p. s. i. g. of nitrogen and brought up to the operating temperature within the range of 200220 C. by means of a heater indicated at 11. The pressure relief valve 13 was then adjusted to maintain a pressure of about 700 p. s. i. g.

A steady rate of air feed of between 4 to 5 standard cubic feet per hour was commenced. An automatic pressure relief valve 13 vents nitrogen, oxides of carbon and a small amount of uncondensed reactant downstream of a condenser 12 to maintain about 700 p. s. i. g. in the reactor.

During a run of 5 hours duration, 500 grams of propylene were fed to the reactor. After termination of the run, the products are recovered by employing any of the Well-known separation techniques, such as a distillation step indicated at 14. The above run produced the following materials, the yields of which are indicated as grams of product per 100 grams of hydrocarbon (propylene) consumed:

, Propylene oxide grams 36.00 Propylene glycol do 16.90 C1 and C2 acids as acetic do 12.20 Polymeric material do 22.60 Carbon oxides do 47.81 Light boiling products do 19.31 Other products Q. do 7.05 Unknown materials do 7.60 Propylene oxide yield percent 26 Propylene glycol yield -do 9 of propylene consumed. In this connection, it hasbeen 3 found that best results are achieved when the mole percent of the propylene in the reaction zone is maintained greater than about of the water-immiscible organic solvent as in the above example.

The importance of olefin concentration is indicated by several experiments wherein it was found that low oxide yields were obtained when the oxidation was carried out in the presence of low concentrations of the olefin. This is illustrated in the following example which is also described in connection with the oxidation of propylene:

Example II A similar oxidation run of propylene was made as in Example I. The same conditions (of temperature, pres sure, solvent, catalyst, inhibitor, etc.) existed here as above. However, the concentration of the propylene in this run was 18.7 mole percent of the amount of solvent whereas the propylene concentration was about 33 mole percent in Example I. The products obtained from the reaction were isolated and determined to exist in the following quantities, indicated as grams of product per 100 grams of propylene consumed:

Propylene oxide grams 12.40 Propylene glycol do 37.20 C1 to C4 acids do 10.68 Polymeric material do 28.60 Carbon oxides do 75.20 Light boiling products do 12.98 Other products do 8.10 Propylene oxide yield "percent" 9 Propylene glycol yield do 30 Thus, from a comparison of the two examples, it can be seen that the propylene oxide yield to a great extent depends on the concentration of the propylene in the Water-immiscible organic solvent. In Example I, the high mole percent of the propylene in the solvent (on the order of about 33) resulted in a propylene oxide yield of about 26% and porpylene glycol yield of only 9%. On the other hand, in Example II, the low mole percent of the propylene in the solvent (on the order of about 18.7) resulted in a propylene oxide yield of only 9% while the yield of propylene glycol was about 30%.

When the process is operated on a continuous basis, the condenser 12 continuously refluxes propylene and other products which are recycled back to the bottom of the reactor 10. Some of the liquid in the reactor 10 is fed to the distillation separation apparatus 14 (which may include several conventional stills) so as to provide for the continuous removal of the propylene oxide, the various oxygenated products and water. The various reaction products are separated from the water-immiscible organic solvent and unreacted propylene which are recycled .to the reactor 10. Substantially all the water is removed from the recycled products so as to maintain a low concentration of water in the oxidation zone.

While one specific example of the present invention has been given above, it is subject to wide variations without departing from the scope thereof. For example, the manganese propionate (of about 0.1% concentration) is a well-known oxidation catalyst. Other manganese salts or salts or oxides of metals of variable valence are equally effective. An important purpose of utilizing an oxidation catalyst is to prevent the creation of large concentrations of dangerously explosive hydroperoxides. It is believed that the metal walls of the reaction chamber may have sufiicient catalytic effect to prevent the formation of such hydroperoxides. Similarly, While the use of a phosphate bufier solution (which is obtained by titrating a solution of trisodium phosphate with phosphoric acid) is quite effective, numerous other well-known buffer solutions may be employed. It is, however, preferable to keep the solution neutral by the addition of appropriate liquid or solid basic materials during the reaction.

The range of operating pressures and operating temperatures is quite broad and can be varied within considerable limits. With regard to pressure, it should be pointed out that it is preferably maintained above 300 pounds per square inch but that considerably higher pressures may be utilized where design considerations indicate the de sirability of such higher pressures. The temperature within the reactor may be varied between about C. and 300 C., the temperature remaining below the critical temperature of the organic solvent in all cases.

While benzene has been illustrated as being a preferred water-immiscible organic solvent, other relatively inert, water-immiscible organic solvents can be used. The preferred organic solvents are those which are inert to oxygen and the olefin oxide, will dissolve large concentrations of the olefin, and are substantially water-immiscible to restrict the quantity of water present in the oxidation zone. Thus, the water-immiscible organic solvent admits but very little, or minute, quantities of water into the oxida tion zone at any one time so that hydrolysis of the formed oxide to the corresponding glycol is minimized at reaction conditions.

When utilizing nitrobenzene as a polymerization inhibitor, it has been found that concentrations of about 10% by weight of the solvent are satisfactory. It is possible that somewhat lower or higher concentrations may be efiective, but it is preferred to operate in the above range. The use of larger quantities of nitrobenzene increases the cost of the operations.

The specific procedure described for the oxidation of propylene to propylene oxide can be applied to other normally gaseous olefins such as the butylenes and the amylenes.

Since certain changes may be made in the above process without departing from the scope of the invention herein involved, it is intended that all matter conained in the above description, or shown in the accompanying drawing, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In the method of forming an olefin oxide by dissolving a normally gaseous monoolefin containing from three to five carbon atoms in a water-immiscible liquid hydrocarbon solvent which is inert to the olefin oxide and passing an elemental-oxygen-containing gas into the solution while the solution is held under pressure and maintained at a temperature above about 130 C., the improvement which comprises maintaining nitrobenzene in the solution to inhibit polymer formation.

2. In the method of forming propylene oxide by dissolving propylene in a water-immiscible liquid hydrocarbon solvent which is inert to propylene oxide and passing an elemental-oxygen-containing gas into the solution while the solution is held under pressure and maintained at a temperature above about 130 C., the improvement which comprises maintaining nitrobenzene in the solution to inhibit polymer formation.

3. In the method of claim 2 wherein the water-immiscible liquid hydrocarbon solvent is benzene.

4. In the method of claim 2 wherein the improvement comprises maintaining in the solution a concentration of nitrobenzene on the order of about 10 percent by weight of the solvent.

References Cited in the file of this patent UNITED STATES PATENTS 2,366,724 Gardner Jan. 9, 1945 2,366,725 Gardner Jan. 9, 1945 2,475,605 Prutton et al. July 12, 1949 2,530,509 Cook Nov. 21, 1950 2,644,837 Schweitzer July 7, 1953 OTHER REFERENCES Chem. Reviews, April 1954, pp. 250 and 287, vol. 54. Boundy-Boyerz Styrene and Its Polymers and Copolymers and Derivatives (1952), p. 21. 

1. IN THE METHOD OF FORMING AN OLEFIN OXIDE BY DISSOLVING A NORMALLY GASEOUS MONOOLEFIN CONTAINING FROM THREE TO FIVE CARBON ATOMS IN A WATER-IMMISCIBLE LIQUID HYDROCARBON SOLVENT WHICH IS INERT TO THE OLEFIN OXIDE AND PASSING AN ELEMENTAL-OXYGEN-CONTAINING GAS INTO THE SOLUTION WHILE THE SOLUTION IS HELD UNDER PRESSURE AND MAINTAINED AT A TEMPERATURE ABOVE AB ABOUT 130*C., THE IMPROVEMENT WHICH COMPRISES MAINTAINING NITROBENZENE IN THE SOLUTION TO INHIBIT POLYMER FORMATION. 